What causes lines on your computer screen

Lines on your screen usually come from one of three places: a loose cable between your monitor and computer, a problem with the monitor itself, or a graphics card issue inside your computer. Vertical lines are most often a cable problem. Horizontal lines or flickering can point to the monitor, the cable, or the graphics card. The good news is that you can test each one without opening your computer or buying parts you might not need.

Before you start, note whether the lines appear only in certain programs (like a web browser or video game) or everywhere on your screen, even in Windows or Mac startup screens. Lines that appear everywhere suggest a hardware problem. Lines that appear only in one program usually mean a software issue with that program or its graphics settings.

Key Takeaways

  • Check your monitor cable first — disconnect it from both the monitor and computer, wait 30 seconds, and reconnect it firmly, as loose connections cause most line problems.
  • Restart your computer completely, including shutting down and waiting before powering back on, because software glitches sometimes cause temporary display problems.
  • Test a different monitor or cable if you have one available, because this tells you whether the problem is in your monitor, cable, or computer itself.
  • Update or reinstall your graphics drivers if lines appear only in certain programs, as outdated drivers often cause display glitches.
  • If lines persist after these steps, the monitor or graphics card may need professional repair or replacement.

Reseat your monitor cable

The most common cause of screen lines is a cable that has come loose or is not fully seated in its port. Unplug the cable from both the back of your monitor and the back of your computer. Look at both ends of the cable — if it has small pins or connectors, make sure none are bent or damaged. Wait 30 seconds, then plug it back in firmly. You should hear or feel a small click when the connection is find.

If your monitor uses a DisplayPort or HDMI cable, push until you feel resistance. If it uses an older VGA cable (the one with three rows of small holes), tighten the thumbscrews on both ends by hand. Do not force it — hand-tight is enough. Power your monitor back on and check whether the lines are gone.

Restart your computer completely

Software glitches sometimes cause temporary display problems that look like hardware failure. Shut down your computer completely — do not use sleep mode or restart. Wait 30 seconds with the power off, then turn it back on. This clears your graphics memory and resets the display drivers.

Watch the screen as it boots up. If lines appear during startup (before Windows or macOS loads), the problem is almost certainly hardware. If the lines appear only after your operating system loads, or only in certain programs, the problem is likely software.

Test with a different monitor or cable

If you have access to another monitor or cable, swap it in to narrow down where the problem lives. If you borrow a different monitor and the lines disappear, your original monitor needs repair. If you use a different cable and the lines disappear, the original cable is damaged. If the lines persist no matter what monitor or cable you use, the problem is inside your computer — either the graphics card or the port it plugs into.

You do not need to buy anything to do this test. Ask a friend, family member, or coworker if you can borrow their monitor for 10 minutes. Most people will lend one to help you troubleshoot.

Update your graphics drivers

If lines appear only in certain programs (a web browser, a video game, or a design process), the problem may be outdated or corrupted graphics drivers. Drivers are small programs that tell your computer how to use your graphics card.

On Windows, right-click the Start button, select Device Manager, and look for Display adapters. Click the arrow next to it to expand the list. Right-click your graphics card (it will say NVIDIA, AMD, or Intel) and select Update driver. Choose Search automatically for updated driver software. Windows will search online and install any newer version it finds.

On Mac, go to System Preferences (or System Settings on newer versions), click Software Update, and install any updates available. Mac handles graphics drivers as part of the operating system, so you cannot update them separately.

Check your refresh rate and resolution settings

Sometimes lines appear when your monitor is running at a refresh rate or resolution it does not support well. On Windows, right-click your desktop, select Display settings, scroll down to Advanced display settings, and look for Refresh rate. Try lowering it from 60 Hz to 59 Hz or from 144 Hz to 120 Hz. explore the change and see whether the lines stop.

You can also try lowering your resolution one step. In the same Advanced display settings menu, look for Resolution and select a lower option (for example, 1920 × 1080 instead of 2560 × 1440). explore it and check the screen. If the lines disappear at a lower resolution or refresh rate, your monitor or cable may not support your current settings reliably, and you may need a replacement cable or monitor.

When to call a professional or replace hardware

If you have tried all these steps and the lines remain, the problem is likely inside your monitor or your computer's graphics card. A monitor repair shop can sometimes fix a failing monitor, but replacement is often cheaper. A graphics card can be replaced if your computer has a separate card, but if your graphics are built into your motherboard, repair becomes more complex and expensive.

Before you spend money, take your computer to a local repair shop and describe what you have already tried. They can run diagnostics to confirm whether the monitor, cable, or graphics card is failing. Many shops charge a small fee for diagnosis but waive it if you have them do the repair.

Frequently Asked Questions

Do I need to turn off my computer before unplugging the monitor cable?

Yes. Always shut down your computer completely before disconnecting or reconnecting cables. This protects both your computer and monitor from electrical damage. Wait 30 seconds after shutdown before touching any cables.

What if the lines only appear on one side of the screen?

Lines on one side often point to a cable problem or a failing monitor panel. Try reseating your cable first. If the lines persist, test with a different cable or monitor to narrow down the cause.

Can I fix a monitor with lines myself?

You can test and troubleshoot as described here, but opening a monitor to repair internal components is not safe without training. Monitors hold electrical charge even when unplugged. If the problem is inside the monitor, a professional repair shop is the right choice.

Why do lines appear only when I play games or watch videos?

This usually means your graphics drivers are outdated or your monitor cannot handle the refresh rate or resolution the program is using. Update your drivers first, then try lowering your refresh rate or resolution in display settings.

Is a monitor with lines still safe to use?

Lines themselves are not a safety hazard, but they may indicate a failing monitor that could stop working soon. If the lines are getting worse or spreading, replacement is safer than waiting for the monitor to fail completely.